The present invention pertains generally to X-ray imaging and more particularly to electronic X-ray imaging using electronic transducers.
Current X-ray imaging systems employ the classical configuration of an X-ray source which projects an X-ray beam through an object to produce an X-ray shadow. The X-ray shadow is cast upon standard photographic film. The film is then processed using standard photographic processing techniques to produce an image of the object. This technique has been in common use since the invention of the modern X-ray tube in 1913 and has changed less in fundamental technology than in applications technique. As a result, users of X-ray equipment must still deal with the cumbersome and expensive use of film and film processing to produce X-ray images using the X-ray diagnostic procedure. Millions of dollars are spent each year on film, chemicals and development processor devices which are used in the hundreds of thousands of X-ray machines employed around the world. This conventional process constitutes an archaic manner of capturing, processing and storing X-ray image information.
Various systems have been developed to overcome the problems and costs associated with film processing. For example, U.S. Pat. No. 4,409,616, entitled "Digital Dental System And Method", issued Oct. 11, 1983, to Ledley discloses a system in which an X-ray tube is inserted in the mouth to produce an X-ray beam which penetrates teeth and other hard tissue in the mouth to produce X-ray shadows which impinge upon an image intensifier, such as a fluorescent screen, to produce a visible image of the hard tissue. A TV camera is mounted adjacent the image intensifier to generate an electronic image of the hard tissue. Although such devices overcome the problems associated with film processing, certain disadvantages are inherent in placement of an X-ray tube within the mouth. For example, a certain amount of patient apprehension may result from the fear of excessive X-ray dosage and the inherent danger associated with the high voltages required to activate the X-ray tube within the mouth.
U.S. Pat. No. 3,932,756, issued Jan. 13, 1976, entitled "X-Ray Detector For A Panoramic X-Ray Device" by Cowell et al. discloses an X-ray detector for converting X-ray energy into electrical energy which contains an X-ray sensitive fluorescent screen optically coupled to photovoltaic energy conversion cells. Although the Cowell et al. invention provides the means for electronically imaging X-ray radiation, the sensitivity of photovoltaic energy conversion cells is extremely low and requires large detectors since the sensitivity of the photovoltaic cell is proportional to the surface area of the cell exposed to optical radiation. Consequently, a resolution comparable to that provided by photographic film cannot be achieved using photovoltaic energy conversion cells or photoconductor cells.
U.S. Pat. No. 4,259,583, entitled "Image Region Selector For A Scanning X-Ray System", issued Mar. 31, 1981, to Albert discloses a system in which a scintillator crystal is disposed within the mouth and scans portions of the oral cavity to be imaged. An external X-ray source produces an X-ray beam which penetrates the mouth to produce X-ray shadows which are detected by the scintillator crystal disposed within the mouth. The optical signal produced by the scintillator crystal is then transmitted to a photomultiplier tube or photodiode for conversion into an electrical energy signal. Again, the resolution of such a system is limited by the size of the scintillator crystals. Multiple scintillator crystals provide a non-uniform response such that accurate image data cannot be readily achieved.
U.S. Pat. No. 3,622,785, entitled "Intraoral Minimal Radiation Fluoroscope", issued Nov. 23, 1971 to Irwin et al. discloses a system in which a curved fiber optic bundle is placed within the mouth to detect X-ray radiation produced by an external X-ray source. Phosphor is deposited on the ends of the fiber optic elements to produce optical energy which is transmitted by the fiber optic bundle to an image intensifier to generate a display image. A vidicon tube produces an electronic signal of the display image. A television monitor is used to produce a visual display of the X-ray image. A clear disadvantage of such a system is that the resolution and contrast of the picture obtained is limited by the image retention characteristics of the phosphor, as well as the diameter of the fiber optic cell needed to carry the phosphor. Additionally, the intensity of the image is directly proportional to the size of the phosphor and the attenuation which occurs over the length of the fiber optic cable.
Consequently, prior art methods of attempting to electronically display X-ray radiation image information have been unable to provide resolution comparable to photographic film imaging techniques in a reliable and cost efficient manner.
Other techniques of scanning and signal processing include:
(1) Sonoda, M. S.; Takano, M. S.; Miyahara, M. S.; Kato, M. S.; Computed Radiography Utilizing Scanning Laser Stimulated Luminescence, Radiology Vol. 148, No. 3 (September, 1983), PA1 (2) Proceedings Two Dimensional Digital Signal Processing Conference in Columbia, MO (Oct. 6-8, 1971), PA1 (3) Leverenz, An Introduction to Luminescence of Solids, RCA Laboratories Division (1950), PA1 (4) Aboutalib, Murphy, Silverman Digital Restoration of Images Degraded by General Motion Blurs, IEEE Transaction on Automatic Control, Vol. ac-22, No. 3 (June 1977), PA1 (5) Cannon, Blind Deconvolution of Spatially Invariant Image Blurs with Phase, IEEE Transactions on Acoustics, Speech, and Signal Processing, Vol. ASSP-24, No. 1, (February 1976), PA1 (6) Trombka, Seltzer A Portable X-Ray Imaging System for Small-Format Applications, Lear Instruments and Methods 158 (1979) 175-180, PA1 (7) Gonzalez, Wintz Digital Image Processing, Addison-Wesley Publishing Company (1977), PA1 (8) Eklundh, Huang, Justusson, Nussbaumer, Tyan, Zohar Two-Dimensional Digital Signal Processing II, Transforms and Median Filters, Springer-Verlag (1981), PA1 (9) American Science and Engineering, Inc. MICRO-DOSE Model 100 X-Ray Inspection System PA1 (10) Rozilri, Virai, Hougelot, Driard, Large Field of View Image Intensifier Gamma Camera Detectors Using a Silicon X Y Scintillation Localizer Thomson CSF, Boulogne, France, PA1 (11) Yin et al. (Nucl. Methods 158: 175, 1979) which discloses the Lixiscope.
These papers are specifically incorporated herein by reference for all that they disclose.